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31.
Ana C.F. Ribeiro Victor M.M. Lobo Hugh D. Burrows Artur J.M. Valente Ana M. Amado Abílio J.F.N. Sobral Ana S.N. Teles Cecília I.A.V. Santos Miguel A. Esteso 《Journal of Molecular Liquids》2008,140(1-3):73-77
Numerical values for the mean distance of closest approach of ions, “a”, for lithium salts in aqueous solutions are presented and discussed. These values were obtained from both experimental activity and diffusion coefficients, and estimated by using different theoretical approaches. 相似文献
32.
33.
Xim Bokhimi Eduardo Muñoz José Luis Boldú Esbaide Adem Octavio Novaro Tessy López Fernando Rojas Ricardo Gómez Amado García-Ruiz 《Journal of Sol-Gel Science and Technology》2000,17(3):219-225
Sol-gel zirconia precursor, zirconium n-butoxide in ter-butanol, was irradiated with 1.3 MeV electrons to a dose of 330 KGy. Gelling was instantaneously produced when an aqueous solution of sulfuric, hydrochloric or acetic acid was added to the irradiated solution; no hydrolysis catalyst was required. Samples were characterized with X-ray powder diffraction, infrared spectroscopy, and electron paramagnetic resonance. The electron irradiation accelerated hydrolysis and condensation, which avoided the stabilization of the tetragonal phase via carboxyls, and decreased the capability of sulfate ions to stabilize it. These results suggest that the stabilization of the tetragonal phase of sol-gel zirconia via carboxyl and sulfate ions depends on their diffusion in the sol. 相似文献
34.
Mariela M. Nolasco Ana M. Amado Paulo J. A. Ribeiro‐Claro 《Journal of Raman spectroscopy : JRS》2010,41(3):340-349
FT‐Raman spectroscopy turns out to be a powerful technique to evaluate the amount of polymorphic and pseudopolymorphic forms in crystalline samples—which is particularly relevant in pharmaceutical sciences. This paper presents a methodology that allows successful quantitative evaluation of the solid‐state hydration and dehydration processes, using FT‐Raman spectroscopy. All the steps required for a reliable evaluation of the hydration/dehydration process are illustrated for the caffeine system, a particularly challenging system presenting limited spectral differences between the pseudopolymorphs. The hydration process of caffeine was found to occur in a single‐step process with a half‐life time of ca 13 h, while the dehydration occurs through a two‐step mechanism. The critical relative humidity was found to be at ca 81 and 42% for anhydrous and hydrate caffeine forms, respectively. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
35.
Antje Klockow H. Michael Widmer Renato Amado Aran Paulus 《Fresenius' Journal of Analytical Chemistry》1994,350(7-9):415-425
The detection limits of the ANTS (8-aminonaphthalene-1,3,6-trisulfonic acid) label and ANTS maltose as a model carbohydrate conjugate were investigated with on-column UV and laser induced fluorescence detection. Under capillary electrophoresis conditions, the concentration and mass detection limits were found to be 5×10–7 mol/l or 8 femtomole with UV and 5×10–8 mol/l or 400 attomole with laser induced fluorescence detection, respectively. Including the derivatization reaction, the best concentration detection limit increases to 1×10–6 mol/l carbohydrate. A model calculation shows that these detection levels are still insufficient to match those of current protein sequencing protocols.Derivatization conditions for dextran and polygalacturonic acid ladders are described with subsequent fast separation in a capillary electrophoresis system under acidic pH buffer conditions. Up to 30 oligomers could be separated in less than 10 min. The application of ANTS labelled carbohydrate analysis in the food industry is demonstrated with the carbohydrate fraction of sweets and the kinetic monitoring of the hydrolysis of polygalacturonic acid.The described ANTS derivitization protocol works with as little as 5 g carbohydrate as demonstrated with a complex oligosaccharide labelled in a reaction volume as little as 2 l. To demonstrate the applicability of this approach to complex carbohydrate analysis, an oligosaccharide mixture derived from human Immunoglobuline G was labelled and separated within 5 min. Separation efficiency and speed are superior to state-of-the-art chromatographic methods. Both electrophoretic and chromatographic methods are complementary because of their different separation mechanism. The implications of using capillary electrophoresis with laser induced fluorescence and appropriate labelling strategies for structural and compositional analysis of complex carbohydrates are discussed.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday 相似文献
36.
Design and validation of a bifunctional ligand display system for receptor targeting 总被引:2,自引:0,他引:2
Chen L Zurita AJ Ardelt PU Giordano RJ Arap W Pasqualini R 《Chemistry & biology》2004,11(8):1081-1091
Here we developed a bacteriophage display particle designed to serve as a bifunctional entity that can target tumors while delivering an agent. We engineered a chimera phage vector containing a pIII-displayed alphav integrins-targeting moiety and a pVIII-displayed streptavidin binding adaptor moiety. By using the chimeric phage particle, targeting of alphav integrins on cells in culture and tumor-related blood vessels was shown through different applications, including luminescent quantum dots localization, surface plasmon resonance-based binding detection, and an in vivo tumor model. The strategy validated here will accelerate the discovery and characterization of receptor-ligand binding events in high throughput, and cell-specific delivery of diagnostics or therapeutics to organs of choice without the need for chemical conjugation. 相似文献
37.
Pedro Domingues M. Rosário M. Domingues Francisco M. L. Amado A. J. Ferrer-Correia 《Journal of the American Society for Mass Spectrometry》2001,12(11):1214-1219
The study of the influence of free radicals in the biological process depends primarily on the capacity to detect these reactive species. In this work we have studied the application of mass spectrometry to the identification of hydroxyl radical species. The detection and identification by collisional activation mass-analyzed ion kinetic energy spectrometry (CA-MIKES) of a spin adduct of DMPO with the hydroxyl radical [(DMPO + O) + H]+ (m/z 130) has demonstrated that mass spectrometry can be a powerful tool in the detection and identification of spin adducts of DMPO with hydroxyl radical species. We were also able to detect the capture of secondary free radicals using ethanol by detecting and identifying the corresponding adduct [(DMPO + ethanol) + H]+. Other spin adducts have also been detected and identified. We consider that the use of mass spectrometry is a relevant technique for the detection of free hydroxyl radicals, especially in complex mixtures, since mass spectrometry is able to discriminate these adducts in such situations. Moreover, using this approach, it was possible to identify new spin adducts. 相似文献
38.
Paulo J. A. Ribeiro-Claro Ana Margarida Amado J. J. C. Teixeira-Dias 《Journal of computational chemistry》1996,17(10):1183-1196
Ab initio molecular geometries and vibrational frequencies of various isolated vanadate species (VO3−4, HVO2−4, H2VO−4, and V2O4−7) were calculated using different pseudopotentials. The relative merits of these were assessed by comparing the calculated molecular parameters with the corresponding values obtained from calculations at all-electron levels and, whenever available, from X-ray studies for the salts. The calculations were extended to higher oligomers (V3O5−10, V4O6−13, and V4O4−12) using the pseudopotential whose basis functions are (10s5p5d)/[2s1p1d] (55/5/5) on vanadium and (4s4p)/[2s2p] (31/31) on oxygen, which yielded the best compromise between accuracy and computational effort. The results indicate a linear centrosymmetric geometry for the isolated V2O4−7 anion. The higher oligomers have less than 180° V(SINGLE BOND)O(SINGLE BOND)V angles, except the noncyclic tetraoligomer which has a linear central V(SINGLE BOND)O(SINGLE BOND)V angle (180°). The cyclic V4O4−12 species presents a planar structure with all the vanadium and bridging oxygen atoms in the same plane. This structure was alrea dy reported for the [(CH3)CNH3][V4O12] salt. The results suggest a lower stability of the linear V4O6−13 species, in agreement with previous reports. © 1996 by John Wiley & Sons, Inc. 相似文献
39.
A. M. Amorim da Costa A. M. Amado M. Becucci Carola Kryschi 《Journal of Molecular Structure》1997,416(1-3):69-73
Phase transition in crystalline pure p-terphenyl and p-terphenyl: tetracene doped crystals was studied with Raman spectroscopy, for temperatures from 295 to 10 K. In particular, the torsional Raman vibrational mode with a “hard-core frequency” of 230.8 cm−1 was investigated in its frequency and bandwidth dependence upon temperature. The results were analyzed based on an order-disorder model allowing the determination of the activation energies and orientational correlation times of the molecular diffusive process in the monoclinic (above 193 K) and triclinic (below 193 K) phases of the crystals. The activation energy is observed to decrease from the monoclinic to the triclinic phase, whereas the orientational correlation times increase, both in the undoped and the doped crystals. The doping of p-terphenyl with tetracene appears to affect the activation energy and the orientational correlation times in a different way in each phase. 相似文献
40.
Conceio Fonseca M. Rosrio M. Domingues Cludia Simes Francisco Amado Pedro Domingues 《Journal of mass spectrometry : JMS》2009,44(5):681-693
The exposure of peptides and proteins to reactive hydroxyl radicals results in covalent modifications of amino acid side‐chains and protein backbone. In this study we have investigated the oxidation the isomeric peptides tyrosine–leucine (YL) and leucine–tyrosine (LY), by the hydroxyl radical formed under Fenton reaction (Fe2+/H2O2). Through mass spectrometry (MS), high‐performance liquid chromatography (HPLC‐MS) and electrospray tandem mass spectrometry (HPLC‐MSn) measurements, we have identified and characterized the oxidation products of these two dipeptides. This approach allowed observing and identifying a wide variety of oxidation products, including isomeric forms of the oxidized dipeptides. We detected oxidation products with 1, 2, 3 and 4 oxygen atoms for both peptides; however, oxidation products with 5 oxygen atoms were only present in LY. LY dipeptide oxidation leads to more isomers with 1 and 2 oxygen atoms than YL (3 vs 5 and 4 vs 5, respectively). Formation of the peroxy group occurred preferentially in the C‐terminal residue. We have also detected oxidation products with double bonds or keto groups, dimers (YL–YL and LY–LY) and other products as a result of cross‐linking. Both amino acids in the dipeptides were oxidized although the peptides showed different oxidation products. Also, amino acid residues have shown different oxidation products depending on the relative position on the dipeptide. Results suggest that amino acids in the C‐terminal position are more prone to oxidation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献